Interpretive Summary: Genetic linkage maps provide the basic framework for the dissection of complex traits in agriculturally important species such as avocado. The most efficient way to produce a genetic linkage map is using molecular markers. A significant number of new molecular markers called microsatellites have been developed in the past few years and these were used to generate a genetic linkage map from progeny of two Florida cultivars 'Simmonds' and 'Tonnage'. Using 715 progeny and 163 markers a linkage map consisting of 12 linkage groups was created. The basic chromosome number for avocado is 12, so each linkage group has been identified. Distances between genetic loci are similar to mile markers on a highway. These distances are called centi-morgans (cM) and the distances ranged from 157.2 cM for linkage group 2 to 2.4 cM for linkage group 12 with a total map length of 1088 cM. This is the first moderately saturated linkage map produced for avocado and it will allow the identification of areas on each linkage group that control horticulturally important traits, such as yield and fruit quality, in the future.

Technical Abstract:
Recent enhancement of the pool of known molecular markers for avocado has allowed the construction of the first moderate density genetic map for this species. Over 300 microsatellite markers have been characterized and 163 of these were used to construct a map from the cross of two Florida cultivars 'Simmonds' and 'Tonnage'. The F1 population consisted of 816 individuals that were analyzed using 135 primer pairs. The microsatellite primers amplified 163 usable loci with 20 amplifying more than one locus. 'Tonnage' was heterozygous for 154 (94%) loci, whereas 'Simmonds' was heterozygous for 66 (40%). Null alleles were identified at several loci. Map construction was accomplished with JoinMap 4.0 using the regression algorithm and Kosambi's mapping function, with a maximum possible recombination coefficient of 0.5. Sub-composite maps were produced for both reciprocal crosses. A composite linkage map was generated for the F1 population by combining data of the reciprocal crosses. The composite map, referred to hereafter as the Florida F1 map, contains 12 linkage groups. Linkage groups ranged in size from 157.3 cM (LG2) to 2.4 cM (LG12) and the number of loci mapped per group ranged from 29 (LG1) to 2 (LG12). The total map length was 1088cM. Only seven markers were observed to have segregation distortion (a=0.05) in common across both sub-composite maps. Phenotypic data from traits of horticultural interest are currently being collected on this population with the ultimate goal of identifying useful quantitative trait loci (QTL) and the development of a Marker Assisted Selection (MAS) program.